In situ extracellular algal organic matter beneficial to the coagulation removal of Microcystis aeruginosa at the stationary growth phase

Cyanobacterial blooms in source water deteriorate drinking water quality. Coagulation process is the first barrier to treat cyanobacteria-laden source water in drinking water treatment plants (DWTPs). The changed growth phase of exponential-stationary of cyanobacteria might affect their coagulation efficiency. However, previous studies mainly conducted coagulation tests using one growth phase of exponential or stationary, and the comparative study is limited. Herein, coagulation tests to remove M. aeruginosa at the exponential and stationary phase were compared using a coagulant of polyaluminum chloride, and factors and mechanisms to differ the coagulation efficiency of M. aeruginosa at the two phases were also investigated. Results showed that the removal efficiency of M. aeruginosa at the stationary phase became higher (3.5-98.4 %) than that at the exponential phase (1.2-94.5 %) with in situ bEOM (binding extracellular organic matter)/dEOM (dissolved extracellular organic matter). The larger and looser flocs were formed at the stationary phase than that at the exponential phase. It could be ascribed to their stronger adsorption inter-bridge and sweeping flocculation via more aromatic/N-containing functional groups in bEOM and molecular-weight of dEOM (>30 kDa) interacted with elevated Al (OH)3(am). These findings provide a deep insight into the coagulation removal of cyanobacterial cells at the two phases. Moreover, this study reveals that these in situ bEOM/dEOM biosynthesized by M. aeruginosa at the sta-tionary phase might be promising bio-flocculants to assist cyanobacterial control at a high efficiency in DWTPs.